Multiple-electrode vacuum tube



April 16, 1929.

F. CONRAD 1,709,659

MULTIPLE ELECTRODE VACUUM TUBE Filed Sept. 27, 1924 INVENTOR ,2 Frank Conrad.

ATTORNEY Patented Apr. 16, 1929.

UNITED STATES 1,109,559 PATENT OFFICE.

FRANK CONRAD, OF PITTSBURGH, PENNSYLVANIA, v ASSIGNOB TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

MULTIPLE-ELECTRODE VACUUM: TUBE.

Application filed September 87, 1924. Serial No. 740,177.

My invention relates to thermionic discharge devices, and more particularly to triode devices.

An object of my invention is to prov de 6 a type of construction for a triode, havmg a higher mutual conductance than triodes of the prior art.

Another object of my invention 1s to construct a triode having a higher plate cur- 1 rent and a lower inter-electrode capacity than triodes of the rior art.

Still another ob ect of my invention is to construct a triode using parts of standard triodes of the prior art which shall 1 have both a higher mutual conductance and a higher plate current than is obtainable in the typeof construction previously used.

Another object of my invention is to construct a thermionic discharge device having a cathode comprising a plurality of filaments, a plurality of grids and a single late.

p Another object of my invention is to produce a thermionic discharge device equivalent to several devices of the prior art connected in arallel without increasing the obj ectionab e inter-electrode capacity proportionately.

Another object of m invention is to produce a thermionic discharge device adapted to be made from standard parts and to occupy no more space than prior devices and to produce results superior to a plural ity of rior devices.

Anot er object, of my invention is to produce a thermionic discharge devicehaving a high plate current, a high mutual conduetance and a low filament potential and filament current value.

In the manufacture of vacuum tubes, it has been found possible to construct a triode in which the cathode consists of 9. treated filament of such size that it can be heated to an operative temperature by the current supply available from a single dry battery.

The construction of this device, however, is subject to rather strict engineering limits. As at present provided, the device has a cathode filament which requiresone-fourth of an ampere at one and one-half volts and which passes a plate current of about 6 milli-amperes at a plate potential of volts. This tube has a mutual conductance of about 350 and it is satisfactory for most radio receiving purposes. It does not, however, satisfactorily operate a loud s eaking telephone receiver at full volume. e demands of current to operate a loud speaker are great enough to overload such a triode. It has been found possible in the prior art to obtain the desired volume from a loud speaker by the expedient of using two or more tubes of the ordinary type in parallel. Increasing the number of tubes in this manner is not always satisfactory by reason of differences of pressure within the tube and to the objectionable increase in inter-electrode capacity.

My invention provides means whereby the equivalent of several tubes of the prior art connected in parallel is produced in a single tube without the objections attending the use of several separate devices.

Other objects and structural details of my invention will be apparent from the following description when read in connection with the accompanying drawing, wherein Figure 1 is an elevational view of a form of my device disclosing the anode structure and other supporting structure; parts being broken away, 7

Fig. 2 is a view similar to Fi re 1 with portions further broken away isclosin a grid and filament construction embodying my invention;

Fig. 3 is a transverse view in section, substantiall above the line III- III of Figs. 1 an 2 showing the electrodes and upper supporting structure of my device;

Fig. 4 is a vertical sectional view substacllatially on the line IVIV of Figure 2; an

Fig. 5 is a top planview of a modified construction of the electrodes of my device.

Referring to the drawing illustrating the 95 construction of a form of my invention, I provide a glass container 1 evacuated to the customary degree of residual pressure, which contains a reentrant portion 2, and a press 3 thereon. Into and through the 100 press 3 are sealed a plurality of lead and support wires or standards 4.

Upon the outer two of the support wires 4 is attached an anode 5. This anode comprises two separate similar parts attached tothe support wires by any convenient means. In the preferred embodiment, they are attached by welding.

Upon another pair of supporting wires 4, that is those next adjacent to and between the pair which support the anode 5, are attached secondary support wires or standards 6, and a plurality of tertiary support wires 7, preferably by welding, to which in turn are attached a plurality of helical grid electrodes 8. To the upper ends of the tertiary support wires 7 is attached another auxiliary support wire or rod 9 which in turn is supported and positioned by a pair of wires 11 and 12 embedded in insulating material members 14 and 15, which are prefcrably of glass and are supported as hereafter described.

To another of wires 4 through press 3 is attached an auxiliary support rod 16, to

.which are attached a plurality of spring members 17 which in turn carry the lower ends of a plurality of longitudinal cathodes in the shape of filaments 18.

- tential.

The upper ends of filaments 18 are attached, by end pieces 19, to another auxiliary support rod 21 which in turn is carried by main support Wires or standards 22 which also are attached to insulating members 14 and 15. Main support wires 22 are further attached to additional wires 4 through the press 3. Likewise, positioning members 23 are inserted in the insulating members 14 and 15 and attached to the upper end of wires 4 which carry the anode 5. The respective electrode species are of similar size and shape, and are positioned within a single container and thus in a common environment. By means of this construction, the operating characteristics of the various triodes are made substantially identical. 3

By reason of this construction, I am able to provide four filamentary cathodes which are positioned in parallel and electrically connected in parallel, thereby bringing conjugate points thereonto a common equipo- I further provide four control electrodes or grids each positioned concentric with and surrounding its respective filament; positioned with the axes thereof parallel with respect to each other and with respect to the filamentsyand, also, electrically connected in parallel and thereby also at equipotential. I further provide a single anode structure surrounding all of the filaments and control electrodes. This single anode is adapted to receive the electron discharge from all of the filaments 4 and is structurally equivalent to four anodes thereabout connected in parallel.

Inthe'operation of my device, the four filaments operate at the usual applied p0- tcntial and each takes the usual cathode current and discharges the usual electron stream. Each grid surrounding each filament performs its usual function of controlling the electron stream and the anode forms the customary function of receiving the anode stream. 'In operation, the filament current required for the total cathode structure is four times that of a single device. Likewise, the plate current is four times that ofthe usual single device, and also the usual change implate current of each device is produced by a given change in potential of the several grids arranged in parallel.

In my device, the amount of current required to produce a given change in grid potential is not perceptiblygreater than the current required to produce a given change of grid potential of an ordinary device. But a given change in grid potential produces four times the change in plate current that would be produced by the same change of grid potential in an ordinary device. This is so because of the fact that there are in effect four complete ordinary devices present.

Since, by definition, the mutual conductance is that change in plate current, measured in milli-amperes, per volt change in grid potential, it will be evident that my device produces a mutual conductance substantially four times the mutual conductance of structures according to the prior art. It will also be observed that this result has been obtained without increasing the highly undesirable inter-electrode capacity proportionately.

In the modification of my invention shown in Fig. 5, the flat sides of the tubular anode 5 have longitudinal folds '31 to form cylindrical compartments individually surrounding the grids 8 associated with the several cathode filamentsof the tubes. The structure of the tube is otherwise the same as that of Figs. 1 to 4:,the several cathode elements being supported by two rods disposed in front of the upper and lower open ends of the tubular anode. The cathodesupporting rods thus serve a double function of mechanically supporting the cathode 'elements and also connecting the same in parallel. Similarly, the four sets of grids surrounding the individual cathodes are supported at both ends of the tubular anode by another pair of rods. The two rods above mentioned, respectively interconnecting the upper ends of the cathodes and the upper ends of the grids, are supported from a pair of axuiliary standards extending outside the tubular anode, one of the standards serving also as a conducting connection to the upper cathode terminals. The tubular anode is supported, at its short ends, on two standards, and the upper ends of the auxiliary standards are anchored to the ends of the anode-supporting standards in order to secure pertect alinement and spacingbetween the several sets of electrodes. This arrangement of the individual sets of electrodes vidual sets of electrodes, which was found very important in tube structures designed to give a low mutual conductance, or a high ratio of amplification factor to plate impedance,

While I have shown only two modifications of my invention in'the accompanying I a. tubular anode,

drawings, it is obviously capable of various changes and modifications without departing from the spirit thereof, and it is desired, therefore, that only such limitations shall be placed thereon as .are imposed by the prior art or indicated in'the appended claims.

I claim as my invention:

1. In anelectron discharge device, a press, a plurality of 'distinct cathode elements disposed within said anode in the direction of the axis thereof, a pluralposed outside of the open upper and lower ends of said anode, respectively, a set of longitudinal cathode elements extending between one set of rods, a setof grid elements respectively surroundin each of said oath-- ode elements and extending between the other set of rods, and a pair of standards extendlng from said press and conductively another standard extending fromsiipporting one ofthe upper rods and in:

,sullatingly supporting the other of the upper evacuated container having a stem, a flat tubular anode, a pair of parallel conducting standards extending from said stem outside said anode, a transverse conducting rod held by and connected to, said stand-. ards above the upper open end of said anode, distinct cathode elements conductively supported b said rod and extending into the interior 0 said anode, a plurality of distinct tubular id elemefits individually surrounding saif cathode elements, a second conducting rod mechanicall supporting and electrically connecting t e upper ends of said grid elements, and insulating members anchoring said standards to said anode and insulatingly su porting said second rod.

1. In an e ectron discharge device, a press, a tubular anode, three or more distinct cathode elements dis osed'within said anode in the direction of t e axis thereof, a plurality of grid members individually surrounding each y of said cathode elements within said anode, a pair of parallel standards extending from said press, a rod supported b said standards above the upper open en of said anode, another standard extending from said press, a second rod su ported by said other standard below t e lower open end of said anode, said cathode elements being supportedby said two sets of rods and connected therethrough in parallel. In testimony whereof, I have hereunto subscribed my name this 4th day of September, 1924.

FRANK CONRAD. 

